The present invention relates to a hand-held belt sander.
Hand-held belt sanders are known in the art. One of such hand held belt sanders is disclosed in the U.S. Pat. No. 4,694,616. It is provided with a driving roller and two deviating rollers having a substantially corresponding diameter. They guide the sanding belt over a sanding base exchangeably arranged on the device. With this device small surfaces of various profiles can be well treated. However, because of the relatively great diameter of the driving and deviating rollers of the hand-held belt sander and because of the coinciding tangential transmission between the rollers and the sanding base, corners and hollow channels are not sufficiently accessible.
The German patent document DE 02 42 26 708 discloses a stationary belt sanding machine with a sanding belt guided over at least two rollers and having a small sanding base. It is provided for sanding works, in which work pieces are to be treated only directly over the sanding belt surface in the embracing region of the rollers, in particular for the production of concave surfaces.
The German patent document DE 0S 39 19 651 discloses a handheld belt sander which in addition to the conventional substantially identical deviating and driving rollers, has a small additional deviating roller for guiding the sanding band tangentially coincidentally between the deviating roller and the sanding base. With this device, corners and hollow channels are substantially better accessible than with other handheld sanders. Since however its construction is based on the conventional handheld belt sander, its belt centering and belt tensioning can be performed in expensive way because of additional, small deviating roller.
Furthermore, the British patent document GB 962 164 discloses a handheld belt sander with the driving roller provided on its periphery with longitudinal grooves. Therefore an improved for transmission to the sanding band is obtained. The handheld belt sander is however heavy, uncomfortable, and complicated.
In the known handheld belt sanders the belt centering is performed by turning or tilting of the deviating rollers which rotate on roller or metal sliding bearings about a fixed rotary point on the roller axis. The deviating roller is mounted by screwing or safety rings on its axle. An exchange of the deviating roller is complicated. Moreover, in the known belt sanding devices the sanding band is tensioned by displacement of an operating lever which is operative for actuating the deviating rollers at the outer side of the sanding belt. However, the operating lever is difficult to axis and not easy to operate.
In belt sanders, independently from their size of the width of the belt, the sanding belt is driven through a rotatable driving roller by a frictional connection. Therefore, the force transmitted to the belt is dependent on the friction value between the inner side of the belt and the roller, as well as on the normal force of the belt on the roller, and on the embracing angle. However, in the known belt sanders these values are not sufficient.
Accordingly, it is an object of present invention to provide a handheld belt sander which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a hand-held belt sander which has a lance-shaped contour, and in which the parts which guide the sanding band are guidingly introduced in a rear region of an elongated housing so that, together with the sanding belt they form in the front region of the housing a centrally forwardly extending, freely projecting wedge-tip shaped contour.
When the hand-held belt sander is designed in accordance with present invention, it has better handling, simplified mechanical system for manual adjustment of a belt centering, as well as is favorable as to the number of individual parts, the manufacture and mounting.
In accordance with another feature of present invention, a fork which receives the deviating roller and which is used for adjustment of the belt running can be exchangeable by a user without dismounting the parts of the device.
A further advantage of the present invention is that the belt running is centerable with a handle which surrounds the roller axis of the deviating roller at both sides and is supported in a sliding member so that it is joined through a virtual three point structure and is tiltable around it with an adjusting screw. The legs of the handle are formed as flat springs which by the screw force both fix the roller and also are used for a special position of the sliding block. The handle is supported at the rear end centrally in the sliding member, so that no high moments are produced in the lever. The small deviating rollers which are arranged in pairs near one another for the belt are composed of high-strength synthetic plastic and run with self lubrication and without additional roller or sliding bearings directly on the roller axle. A substantially simplified mounting, lower number of components, and low cost, as well as a simpler subsequent change of the deviating rollers is characteristic for the inventive solution when compared with the known solutions.
A special advantage of the inventive hand-held belt sander is that the sanding belt can be easily exchangeable by unlocking of both clamping rollers with a single lever which is easily operable and arranged outside of the device. The both clamping rollers are supported so that they are elastically coupled with one another to be outwardly radially expandable. In the locked position this provides for the elastic sufficient belt clamping. The adherence of the sanding dust is prevented by the clamping rollers. The clamping lever is designed so that both in the blocked and in the unblocked position it engages in a simple manner without additional components for arresting its rotary axle.
A further advantage is that a fixed base plate of the belt clamping mechanism and the sanding shoe, as well as other parts are held premountable before the mounting in the ridge-like manner. In addition, the base plate which works as a supporting cover has further functions such that the receipt of the roller bearing of the drive shaft which carries the driving roller and the receipt end positioning of the buffer disk. The bearing support is formed as a simple punched part for all multiple functions. Since its mounting is performed without additional parts between the sliding shoe and the housing shell, only a few individual components are and the mounting is simplified. A further advantage of the invention is that the frictional connection of the driving roller relative to the sanding belt is increased by combining the running surface of the driving roller from hard and soft material and applying grain material on the running surface, or it is provided with brushes and the normal force between the sanding belt and the driving roller is increased by forming grooves in the running layer, so that inclined small plates are formed which are placed under load and thereby increase in diameter of the roller. Furthermore, the application of a skin-like coating has the advantage that under load it rises, and an additional pressing roller is arranged, so that with no raising the clamping force of the belt is needed and the sanding belt can be finally operated.
It is also advantageous to provide a form-locking connection between the belt and the roller, by combining a perforated belt with a roller provided with pins or by profiling the lower side of the belt and the roller so that a form-locking connection is produced during roller of this parts over one another. In corresponding variants, the advantage of a form-locking drive is provided by a transmitting correspondingly high forces with relatively low belt clamping.
Therefore the sanding shoe, the drive cover, the housing and the means for belt clamping are provided with inventive features, and the sanding shoe and the drive cover form an important component of a replacement part, on which a differently equipped sanding belts or the like can be arranged.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.